For many years anchor nail fasteners of the type shown in the aforesaid U.S. Letters Patent have been and are still being used successfully in built-up roof construction (termed B.U.R. in the trade) to hold insulation and roofing paper or the like on low-density roof decks. In constructing a B.U.R. using the anchor nail fasteners of the aforesaid patents, a fastener length is selected such that the tube portion extends completely through the insulation or other covering and into the underlying low density roof deck with the large head on the tube overlying the insulation or other covering to be retained on the deck. An anchoring nail insert is then driven down into the tube portion and its pointed end strikes a target or ramp near the lower end of the tube and curves out the side of the tube through an opening therein and is imbedded in the roof deck to securely hold the large head of the tube against the insulation or other covering, thereby retaining the same against the roof deck. After the insulation or other covering has been secured in this fashion, several layers of roofing felt or tar paper, together with applications of hot asphalt are applied thereover to seal the roof against the weather. Thus, a roof is built up covering the insulation and the heads of the anchor nail fasteners.
In recent years B.U.R. roof construction has been replaced in many instances by the so-called single ply memberane or thin film. Instead of laying down several layers of roofing felt or tar paper with intermediate coatings of hot asphalt, a single moisture barrier film is laid down over the insulation and over the fastener heads. The film may be as thin as 0.009 inches in some instances, while other types may range from 0.030 inches to 0.072 inches in thickness. Some of these films have little capability to stretch with movement of the building, and others, though quite stretchable, are so thin that they may be easily punctured. In either event, the anchor nail fastener must maintain a low profile and not project upwardly in such fashion as to cause a puncture of the film.
What has occurred, unfortunately, is that in some instances the anchor nail insert, though driven down securely in the tube, has popped back up slightly after the single ply membrane has been applied over the roof, and then through movement of the building causing the upwardly protruding head of the anchor nail insert to abrade the film, or by a person walking on the film and pressing it down at the popped-up anchor nail insert, the film has been ruptured, allowing moisture to creep beneath the film and eventually into the building. This problem has been so serious that the anchor nail fasteners of the type shown in the aforementioned patents have not been used with a single ply roof construction, and this has substantially reduced sales of these fasteners in today's market.
After considerable investigation, I discovered that the pop-back seemed to occure more often where the density of the roof deck was low. For example, in retrofitted roofs, the density of the decks is less than originally and pop-back was a frequent occurrence. In some new constructions, roof deck materials are being used of a lower density than in the past, or, as sometimes occurs, at the specific location where the insert curls into the deck there is a void in the deck.